[unreadable] Electrospray fourier transfer mass spectrometry (ESI-FTMS) provides a powerful tool for analysis of covalent modifications of proteins. This proposal applies ESI-FTMS for the detection of transient covalent modifications of non-ribosomal-petide synthetases (NRPS) and polyketide synthases. Initially, a general protocol will be developed for the rapid identification of the acyl domains. Subsequently, this method will be extended to the identification of the in vivo or in vitro "preferred" substrates for acyl domains. This method will then be applied to the identification of the substrate(s) for the calE8 gene product involved in the biosynthesis of the antitumor agent calicheamycin, a PKS for which we do not know the substrate. Finally, ESI-FTMS will be used for the kinetic characterization of the NRPS found in the biosynthesis of the aminocoumarin antibiotics coumeramycin and clorbiocin while the substrates are still connected to their acyl domains. [unreadable] [unreadable]